On-Bed Differential Piezoelectric Sensor

ABSTRACT

A sensor system includes a sensor stack, a differential amplifier, an analog-to-digital converter, and a processor. The sensor stack includes a piezoelectric material having a first side opposing a second side, a first electrode connected to the first side, and a second electrode connected to the second side. The differential amplifier is coupled to the first and second electrodes and is configured to generate a differential output indicative of vibrations sensed by the piezoelectric material. The analog-to-differential converter is configured to digitize the differential output. The processor is configured to identify a type of biological vibration included in the digitized differential output.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a nonprovisional of and claims the benefit under 35 U.S.C. 119(e) of U.S. Provisional Patent Application No. 62/885,028, filed Aug. 9, 2019, and U.S. Provisional Patent Application No. 62/891,195, filed Aug. 23, 2019, the contents of which are incorporated herein by reference as if fully disclosed herein.

FIELD

The described embodiments relate generally to an on-bed differential piezoelectric sensor, or to a sensor system including such a sensor. The sensor or sensor system can be used on a bed or elsewhere to sense vibrations, including sounds. The sensed vibrations or sounds may include biological vibrations or sounds made by a user, such as heart vibrations or sounds, lung vibrations or sounds, nasal vibrations or sounds, or digestive vibrations or sounds.

BACKGROUND

A device such as a smartphone or electronic watch may include various health sensors. The health sensors may be capable of monitoring a user's heart rate, heart rhythm, steps taken, calories burned, and so on as the user carries the smartphone or wears the electronic watch during the day. However, at night, the user may place (or couple) the smartphone and electronic watch on (or to) one or more chargers. The user's nighttime health may therefore not be monitored, or may be monitored to a lesser extent than the user's daytime health. Although the user may place the smartphone on their bed or wear the electronic watch while sleeping, these options may not be comfortable or convenient, and may interfere with charging these devices.

SUMMARY

Embodiments of the systems, devices, methods, and apparatus described in the present disclosure are directed to sensors and sensor systems for differentially sensing vibrations, such as biological vibrations or sounds made by a user. Biological vibrations and sounds include, for example, heart vibrations or sounds, lung vibrations or sounds, nasal vibrations or sounds, and digestive vibrations or sounds. Vibrations and sounds are collectively referred to herein as vibrations, and may include audible sounds (e.g., sounds heard by a person) and inaudible sounds (e.g., sounds experienced as vibrations and not heard by a person, or sounds heard or sensed by a device configured to listen or monitor for such sounds). In some embodiments, a sensor may be placed on a user's bed, or otherwise positioned on or near the user's torso. The sensor may include a piezoelectric material or element having electrodes connected to opposite sides thereof. Vibration-induced waveforms (e.g., waveforms associated with biological vibrations or sounds) may impinge on the piezoelectric material and impart forces on the piezoelectric material, which forces cause the piezoelectric material to change shape and vibrate. The electrodes connected to the piezoelectric material may differentially sense these vibrations (i.e., the electrodes may produce out-of-phase signals in response to the vibrations, as a result of the electrodes being connected to opposite sides of the piezoelectric material). When the signals generated by the electrodes are differentially amplified and subtracted, the out-of-phase signals combine to produce an amplified waveform (e.g., an amplified vibratory or audio output). In contrast, electromagnetic noise sensed by the electrodes (e.g., AC line noise) may induce in-phase signals that combine with out-of-phase signals. However, when the signals generated by the electrodes are differentially amplified and subtracted, the in-phase noise signals cancel out, leaving only an amplified signal (e.g., an amplified vibratory or audio output).

In a first aspect, the present disclosure describes a sensor system that includes a sensor stack, a differential amplifier, an analog-to-differential converter, and a processor. The sensor stack may include a piezoelectric material having a first side opposing a second side, a first electrode connected to the first side, and a second electrode connected to the second side. The differential amplifier may be coupled to the first and second electrodes and be configured to generate a differential output indicative of vibrations sensed by the piezoelectric material. The analog-to-differential converter may be configured to digitize the differential output. The processor may be configured to identify a type of biological vibration included in the digitized differential output.

In another aspect, the present disclosure describes a sensor system that includes a sensor, an electrical interconnect, and a differential amplifier. The sensor may include a piezoelectric element, and first and second electrodes that are respectively connected to first and second opposing surfaces of the piezoelectric element. The electrical interconnect may include first and second conductors, respectively connected (or connectable) to the first and second electrodes. The differential amplifier may be connected (or connectable) to the first and second conductors and provide a differential output indicative of vibrations sensed by the piezoelectric element.

In another aspect of the disclosure, the present disclosure describes a method of monitoring biological vibrations of a user. The method may include receiving a pair of signals from a pair of electrodes connected to opposite sides of a piezoelectric element; differentially amplifying the pair of signals to generate a differential output; identifying a type of biological vibration included in the differential output; and outputting an indicator of the type of biological vibration.

In addition to the aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the drawings and by study of the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which:

FIG. 1 shows an example of a sensor system that may be used to sense biological vibrations;

FIG. 2 shows an alternative embodiment of the vibration sensor described with reference to FIG. 1;

FIG. 3 shows examples of some different types of biological vibrations that can be sensed by the vibration sensors described with reference to FIG. 1 or 2, and the approximate frequency ranges of such vibrations;

FIG. 4 shows example vibration patterns for ballistocardiography (BCG)/seismocardiography (SCG) vibrations or sounds; S1, S2, S3, and S4 heart sounds; heart murmurs; normal lung sounds; wheeze sounds; crackle sounds; snore sounds; cough sounds; and respiration sounds;

FIG. 5 shows an example embodiment of various components included in the sensor system described with reference to FIG. 1;

FIG. 6 illustrates how measured vibrations, including biological vibrations, may be amplified by the processing circuitry described with reference to FIGS. 1 and 5, while an AC line frequency or other background noise may be canceled by the processing circuitry;

FIG. 7A shows, in exploded form, an example more detailed cross-section of the sensor stack described with reference to FIG. 5;

FIG. 7B shows the cross-section of FIG. 7A in assembled form;

FIG. 7C shows, in exploded form, an example of the sensor interface described with reference to FIG. 5, in the context of the sensor stack described with reference to FIG. 7A;

FIG. 8A shows an example more detailed cross-section of the sensor stack described with reference to FIG. 7A;

FIGS. 8B-8D show various examples of the sensor interface described with reference to FIG. 5, in the context of the sensor stack described with reference to FIG. 8A; and

FIG. 9 illustrates a method of monitoring biological vibrations of a user.

The use of cross-hatching or shading in the accompanying figures is generally provided to clarify the boundaries between adjacent elements and also to facilitate legibility of the figures. Accordingly, neither the presence nor the absence of cross-hatching or shading conveys or indicates any preference or requirement for particular materials, material properties, element proportions, element dimensions, commonalities of similarly illustrated elements, or any other characteristic, attribute, or property for any element illustrated in the accompanying figures.

Additionally, it should be understood that the proportions and dimensions (either relative or absolute) of the various features and elements (and collections and groupings thereof) and the boundaries, separations, and positional relationships presented therebetween, are provided in the accompanying figures merely to facilitate an understanding of the various embodiments described herein and, accordingly, may not necessarily be presented or illustrated to scale, and are not intended to indicate any preference or requirement for an illustrated embodiment to the exclusion of embodiments described with reference thereto.

DETAILED DESCRIPTION

Reference will now be made in detail to representative embodiments illustrated in the accompanying drawings. It should be understood that the following description is not intended to limit the embodiments to one preferred embodiment. To the contrary, it is intended to cover alternatives, modifications, and equivalents as can be included within the spirit and scope of the described embodiments as defined by the appended claims.

Described herein are techniques that enable the high-fidelity collection of biological vibrations, such as heart vibrations or sounds, lung vibrations or sounds, nasal vibrations or sounds, or digestive vibrations or sounds. The collection of chest cavity vibrations, in particular, such as heart and lung vibrations or sounds, typically requires a sensing bandwidth of at least 500 Hertz (Hz). Unfortunately, the bandwidth includes typical AC line frequencies, which are in the range of 50/60 Hz, and which can have second harmonics in the range of 100/120 Hz (e.g., due to rectification of the AC line frequencies in power supplies). To provide high-fidelity sensing of chest cavity vibrations (and/or other biological vibrations), while mitigating the effects of line noise interference, the techniques described herein employ differential sensing. Differential sensing is useful in that it produces out-of-phase signals corresponding to mechanical vibrations, such as biological vibrations, and the out-of-phase signals constructively interfere and amplify mechanical vibrations (e.g., biological vibrations) when subtracted. In contrast, electromagnetic noise (e.g., AC line noise) that may interfere with the sensing process produces in-phase signals (i.e., common mode signals). When subtracted, the in-phase signals cancel out (through destructive interference), leaving an amplified output corresponding to the sensed mechanical vibrations.

These and other techniques are described with reference to FIGS. 1-9. However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for explanatory purposes only and should not be construed as limiting.

Directional terminology, such as “top”, “bottom”, “upper”, “lower”, “front”, “back”, “over”, “under”, “left”, “right”, etc. is used with reference to the orientation of some of the components in some of the figures described below. Because components in various embodiments can be positioned in a number of different orientations, directional terminology is used for purposes of illustration only and is in no way limiting. The directional terminology is intended to be construed broadly, and therefore should not be interpreted to preclude components being oriented in different ways. The use of alternative terminology, such as “or”, is intended to indicate different combinations of the alternative elements. For example, A or B is intended to include, A, or B, or A and B.

FIG. 1 shows an example of a sensor system 100. The sensor system 100 may be used to sense biological vibrations (e.g., chest cavity vibrations or sounds, nasal cavity vibrations or sounds, abdominal cavity vibrations or sounds, and so on) made by a person laying on a bed 102, a couch, an examination table, or the like. Alternatively, the sensor system 100 may be used by a person sitting in a chair, or by a person who has attached part or all of the sensor system 100 (e.g., the sensor package 104) to their torso, or to an object in contact with their torso. In addition to biological vibrations, the sensor system 100 may sense other mechanical vibrations.

In some embodiments, the sensor system 100 may include a vibration sensor 110 that is coupled to processing circuitry 114 by an electrical interconnect 108. In some embodiments, the vibration sensor 110 may be housed in a sensor package 104, the processing circuitry 114 may be housed in a processing module 106 (e.g., a separate physical package, such as a dongle), and the electrical interconnect 108 may take the form of an electrical cord or cable that connects the vibration sensor 110 to the processor 114. Alternatively, the electrical interconnect 108 may take the form of wires, conductive traces, or other conductive elements, which conductive elements may be routed within one or more connectors, on one or more substrates (e.g., on or in a printed circuit board (PCB) or integrated circuit (IC)), or on or within the vibration sensor 110. In some embodiments, the vibration sensor 110, electrical interconnect 108, and processing circuitry 114 may all be housed within the sensor package 104 and, in some of these embodiments, there may not be a separate housing for the processing circuitry 114 or electrical interconnect 108 (e.g., there may not be a physically separate processing module 106 or electrical cord).

The sensor package 104, including the vibration sensor 110, may be flexible, so that it is more or less unnoticeable to a person laying on the bed 102. The electrical interconnect 108 may also be flexible, and/or the processing circuitry 114 may be flexible (e.g., the processing circuitry 114 may be formed on or in a flexible substrate). In some embodiments, one or more of the vibration sensor 110, electrical interconnect 108, processing circuitry 114, or sensor package 104 may not be flexible.

The processing circuitry 114 may receive and process signals received from the vibration sensor 110 (e.g., signals received via the electrical interconnect 108). For example, the processing circuitry 114 may amplify and digitize signals received from the vibration sensor 110. In some embodiments, the processing circuitry 114 may include a communications interface for communicating digitized signals or other information to another device 112 (e.g., a remote device), such as a smartphone or electronic watch. The communications interface may also receive from the other device 112. For example, the communications interface may receive instructions, control signals, settings, or queries from the other device 112. The communications interface may be wireless (e.g., a Wi-Fi or Bluetooth interface) or wired (e.g., a universal serial bus (USB) interface). In some cases, the processing circuitry 114 may include a processor (e.g., a microprocessor, a microcontroller, an application-specific integrated circuit (ASIC), or a field-programmable gate array (FPGA)). The processor may control operation of other circuitry, such as the circuity that processes signals received from the vibration sensor 110, or the communications interface. In some cases, the processing circuitry 114 may additionally or alternatively include circuits that do not rise to the level of a processor. The processing circuitry 114 may be housed separately from the vibration sensor 110, such as in a processing module 106. Alternatively, the processing circuitry 114 may be housed with the vibration sensor 110 in the sensor package 104, or components of the processing circuitry 114 may be distributed between different physical locations (e.g., a portion of the processing circuitry 114 may be housed with the vibration sensor 110 and a portion of the processing circuitry 114 may be housed in a separate processing module 106). In some cases, part or all of the processing circuitry 114 may be integrated with the vibration sensor 110 on a shared substrate. In some embodiments, components or functions of the processing circuitry 114 may be housed by, or provided by, the remote device 112, and the electrical interconnect 108 may terminate at a connector that plugs into the remote device 112. The electrical interconnect 108 may also terminate at a connector that plugs into the processing module 106.

The sensor package 104 may variously enclose the vibration sensor 110, and/or protect the vibration sensor 110 from dust, oil, moisture, or liquid spills, and/or electrically insulate the vibration sensor 110 from a user. In some embodiments, the sensor package 104 may be made of natural or synthetic cloth, plastic, or other materials, and may include a sealed or accessible pouch configured to hold the vibration sensor 110. In some cases, the sensor package 104 may be a pocket included in (or attachable to) a bed sheet, mattress, cushion, or seating surface. In some embodiments, the sensor package 104 may include a polymer, thermoplastic polymer, resin, or other material that is applied to, encapsulates, or is molded around the vibration sensor 110. In some embodiments, the sensor package 104 may include both an inner package (e.g., a material that is applied to, encapsulates, or is molded around the vibration sensor 110) and an outer package (e.g., a cloth or plastic sleeve or cover). When the electrical interconnect 108 is packaged in an electrical cord, the sensor package 104 may have an opening through which the electrical cord may pass. When part or all of the processing circuitry 114 is separately housed in the processing module 106, the processing module 106 may be constructed similarly to, or different from, the sensor package 104. In some embodiments, the processing module 106 may take the form of a polymer (e.g., plastic) housing.

FIG. 2 shows an alternative embodiment of the vibration sensor described with reference to FIG. 1. In particular, the vibration sensor 200 shown in FIG. 2 includes a plurality of vibration sensors 202-1, 202-2, 202-3, 202-4, each of which may be configured similarly to the vibration sensor 100. The vibration sensors 202-1, 202-2, 202-3, 202-4 may be encapsulated in a flexible material 204 at predefined positions (e.g., in an array or other distribution pattern); held in different pockets of a sensor package (e.g., a sensor package having multiple pockets for the multiple vibration sensors 202-1, 202-2, 202-3, 202-4); or arbitrarily positioned on a bed or other surface by their user or an aide (e.g., a partner, caretaker, or nurse). In use, each vibration sensor 202-1, 202-2, 202-3, 202-4 may be positioned at a different location and/or oriented in a different direction with respect to a user's torso.

Each vibration sensor 202-1, 202-2, 202-3, 202-4 may be positioned or used to sense the same or different biological vibrations (e.g., chest cavity vibrations or sounds, nasal cavity vibrations or sounds, abdominal cavity vibrations or sounds, and so on). For example, two or more vibration sensors 202-1, 202-2, 202-3, 202-4 may be positioned to sense the same biological vibrations (e.g., lung vibrations or sounds), and their outputs may be compared or combined. Additionally or alternatively, and by way of example, one or more of the vibration sensors 202-1, 202-2, 202-3, 202-4 may be positioned to sense chest cavity vibrations or sounds (e.g., one or more vibration sensors may be positioned closer to a user's chest cavity), and one or more different vibration sensors 202-1, 202-2, 202-3, 202-4 may be positioned to sense abdominal cavity vibrations or sounds (e.g., one or more vibration sensors may be positioned closer to a user's abdomen). Or, for example, one or more vibration sensors 202-1, 202-2, 202-3, 202-4 may be positioned to sense heart vibrations or sounds (e.g., one or more vibration sensors may be positioned closer to a user's heart), and one or more other vibration sensors 202-1, 202-2, 202-3, 202-4 may be positioned to sense lung vibrations or sounds (e.g., one or more vibration sensors may be positioned closer to a user's lungs). In some embodiments, the vibration sensors 202-1, 202-2, 202-3, 202-4 may all have the same configuration, and may simply be placed closer to, or farther from, different portions of a user's torso. In other embodiments, different vibration sensors may be longer, wider, or differently shaped, to improve their sensitivity to particular types of vibration, or to improve their sensitivity to vibrations originating from particular regions of a user's torso.

The vibration sensors described with reference to FIGS. 1 and 2 can be used to differentially sense various types of biological sounds. As previously discussed, the sensing of biological sounds using differential sensing can enable the sensing of sounds having a frequency bandwidth that includes (e.g., intersects or crosses) an alternating current (AC) line frequency, or sounds on both sides of an AC line frequency (e.g., low-frequency vibrations and higher frequency audible sounds).

The biological vibrations sensed by the vibration sensors described with reference to FIGS. 1 and 2 may include vibrations or sounds that propagate through a person and/or other objects that are directly or indirectly in contact with the vibration sensors. In this manner, ambient sounds may not be sensed, as might be the case with a typical diaphragm-type microphone included in a smartphone or electronic watch.

FIG. 3 shows examples of some different types of biological vibrations that can be sensed by the vibration sensors described with reference to FIGS. 1 and 2, and the approximate frequency ranges of such vibrations.

A first set of biological vibrations that can be sensed are heart vibrations or sounds. Heart vibrations and sounds include, for example, BCG/SCG vibrations and sounds 300 extending from about 5 Hz-50 Hz; S1, S2, S3, and S4 heart sounds 302 extending from about 25 Hz-250 Hz; and heart murmurs 304 (including different types of heart murmurs) extending from about 100 Hz-1 kilohertz (kHz). Both the BCG/SCG vibrations and sounds and S1, S2, S3, and S4 heart sounds may have frequency bandwidths that intersect or cross an AC line frequency (e.g., 50/60 Hz). A differential sensor can subtract out the AC line frequency during signal amplification, as discussed with reference to FIG. 7.

A second set of biological vibrations that can be sensed are lung vibrations or sounds. Lung vibrations and sounds include, for example, normal lung sounds, wheeze sounds, crackle sounds, and cough sounds, which generally have frequency bandwidths above AC line frequencies, and respiration vibrations, which generally have frequency bandwidths below AC line frequencies. Normal lung sounds 306 (e.g., vesicular sounds) may generally extend from about 100 Hz-1 kHz; wheeze sounds 308 may generally extend from about 100 Hz-5 kHz; crackle sounds 310 may generally extend from about 300 Hz-700 Hz; and cough sounds 312 may generally extend from about 275 Hz-600 Hz. Respiration vibrations (e.g., inspiration and expiration vibrations) 314 are generally in the 1 Hz-2 Hz range, and are typically not audible to the human ear.

A third set of biological vibrations that can be sensed are nasal vibrations or sounds. Nasal vibrations and sounds include, for example, snore sounds. Snore sounds 316 may generally extend from about 130 Hz-1250 Hz.

In some cases, a type of biological vibration that is sensed by a differential sensor (or different types of biological vibrations) can be distinguished by virtue of the frequency bandwidth in which it resides. Alternatively, biological vibration types can be distinguished by their vibration patterns; by a combination of their frequency bandwidth and vibration pattern; or using alternative or additional parameters (e.g., peak-to-peak timings, peak-to-peak intensities, and so on). FIG. 4 shows examples vibration patterns 400 for BCG/SCG vibrations; S1, S2, S3, and S4 heart sounds; heart murmurs; normal lung sounds; wheeze sounds; and crackle sounds. As shown, the vibration patterns for the different biological sound types typically vary, and sometimes substantially.

FIG. 5 shows an example embodiment of various components included in the sensor system described with reference to FIG. 1. In particular, FIG. 5 shows examples of the vibration sensor 110, electrical interconnect 108, and processing circuitry 114.

As shown, the vibration sensor 110 may include a sensor stack 500 (e.g., a plurality of elements or layers, such as a plurality of planar elements or layers, stacked one on top of the other). At its core, the sensor stack 500 may include a piezoelectric material 502 (e.g., a piezoelectric element). In some embodiments, the piezoelectric material 502 may include a polyvinylidene difluoride (PVDF) material, such as a PVDF film, a PVDF-copolymer, a PVDF/poly-L-lactide (PLLA) blend, and so on. The piezoelectric material 502 may alternatively include a PLLA material or other material. The piezoelectric material 502 may have first and second opposing sides 504-1, 504-2 and surfaces that extend in a plane perpendicular to the stack 500.

A first electrode 506-1 (e.g., a positive electrode) may be connected to the first side 504-1 or surface of the piezoelectric material 502, and a second electrode 506-2 (e.g., a negative electrode) may be connected to the second side 506-2 or surface of the piezoelectric material 502. The first and second electrodes 506-1, 506-2 may terminate at a sensor interface 508 that passively outputs a pair of signals obtained from the piezoelectric material 502 by the first and second electrodes 506-1, 506-2. The electrical interconnect 108 may be permanently or detachably connected to the sensor interface 508.

Optionally, the sensor stack 500 may further include a first electromagnetic noise shield 510-1 (e.g., a first ground layer) disposed on the first side 504-1 of the piezoelectric material 502. The first electromagnetic noise shield 510-1 may be electrically insulated from both the piezoelectric material 502 and the first electrode 506-1, with the first electrode 506-1 disposed between the piezoelectric material 502 and the first electromagnetic noise shield 510-1. The sensor stack 500 may also include a second electromagnetic noise shield 510-2 (e.g., a second ground layer) disposed on the second side 504-2 of the piezoelectric material 502. The second electromagnetic noise shield 510-2 may be electrically insulated from both the piezoelectric material 502 and the second electrode 506-2, with the second electrode 506-2 disposed between the piezoelectric material 502 and the second electromagnetic noise shield 510-2.

In some embodiments, a first thermoplastic polymer resin 512-1 (e.g., a first layer of polyethylene terephthalate (PET) or biaxially-oriented PET (BoPET)) may be disposed between the first electrode 506-1 and the first electromagnetic noise shield 510-1, and a second thermoplastic polymer resin 512-2 (e.g., a second layer of PET or BoPET) may be disposed between the second electrode 506-2 and the second electromagnetic noise shield 512-2.

In some embodiments, the outermost or exterior layers (and in some cases sides) of the stack 500 may include a third thermoplastic polymer resin 514-1 (e.g., a third layer of PET or BoPET) disposed on or over the first electromagnetic noise shield 510-1, and a fourth thermoplastic polymer resin 514-2 (e.g., a fourth layer of PET or BoPET) disposed on or over the second electromagnetic noise shield 510-2. The third and fourth thermoplastic polymer resins 514-1, 514-2 may be considered first and second non-conductive stack covers for the vibration sensor 110. In other embodiments, the electromagnetic noise shields 510-1, 510-2 may be the outermost or exterior layers of the stack 500, or the first and second thermoplastic polymer resins 512-1, 512-2 may be the outermost or exterior layers of the stack 500.

The first and second thermoplastic polymer resins 512-1, 512-2 may be coupled to the first and second electrodes 506-1, 506-2 using a pressure-sensitive adhesive (PSA) (e.g., a PSA deposited on each of the first and second electrodes 506-1, 506-2, or on each of the first and second thermoplastic polymer resins 512-1, 512-2, and/or between corresponding ones of the first and second electrodes 506-1, 506-2 and first and second thermoplastic polymer resins 512-1, 512-2). Similarly, the third and fourth thermoplastic polymer resins 514-1, 514-2 may be coupled to the first and second electromagnetic noise shields 510-1, 510-2 using a PSA (e.g., the same type of PSA used to couple the first and second thermoplastic polymer resins 512-1, 512-2 to the first and second electrodes 506-1, 506-2, or a different type of PSA), which PSA may be deposited on each of the first and second electromagnetic noise shields 510-1, 510-2, or on each of the third and fourth thermoplastic polymer resins 514-1, 514-2, and/or between corresponding ones of the first and second electromagnetic noise shields 510-1, 510-2 and third and fourth thermoplastic polymer resins 514-1, 514-2).

Any of the thermoplastic polymer resins 512-1, 512-2, 514-1, 514-2 may alternatively be replaced with a different type of electrical insulator.

In some embodiments, the elements or layers stacked on either side of the piezoelectric material 502 may be symmetric or nearly symmetric on opposite sides 504-1, 504-2 of the piezoelectric material 502 (e.g., the silhouettes of corresponding elements or layers may have a symmetric projection over 90% or more of their circumference). For example, the first and second electrodes 506-1, 506-2 may be symmetric or nearly symmetric, the electromagnetic noise shields 510-1, 510-2 may be symmetric or nearly symmetric, the thermoplastic polymer resins 512-1, 512-2 may be symmetric or nearly symmetric, and the thermoplastic polymer resins 514-1, 514-2 may be symmetric or nearly symmetric. In addition, the electromagnetic noise shields 510-1, 510-2 may have surface areas that are greater than the surface areas of the electrodes 506-1, 506-2. In some embodiments, the electromagnetic noise shields 510-1, 510-2 may completely cover the surface areas of the electrodes 506-1, 506-2. In some embodiments, the electromagnetic noise shields 510-1, 510-2 may cover most of the surface areas of the electrodes 506-1, 506-2, but nonetheless have surface areas that are greater than the surface areas of the electrodes 506-1, 506-2. This helps to mitigate or eliminate the inducement of common mode noise in the electrodes 506-1, 506-2.

The electrical interconnect 108 may mechanically and electrically connect to the sensor interface 508, and may include first and second conductors 516-1, 516-2 that connect to the first and second electrodes 506-1, 506-2 at or via the sensor interface 508. The first and second conductors 516-1, 516-2 may be surrounded by insulation, and may be twisted to form a twisted pair within the electrical interconnect 108. The first and second electromagnetic noise shields 510-1, 510-2 may be connected to each other and to an electromagnetic noise shield 518 (e.g., a metal or conductive sheath) that surrounds the first and second conductors 516-1, 516-2, thereby forming a shielded twisted pair (STP). The electromagnetic noise shield 518 may be surrounded by a non-conductive sheath (not shown). In alternative embodiments, the first and second conductors 516-1, 516-2 may be routed on a substrate as conductive traces, with a noise shield being formed by conductive traces or planes coupled to the first and second electromagnetic noise shields 510-1, 510-2.

The processing circuitry 114 may include components that form part of an analog front end (AFE) and/or data acquisition (DAQ) circuit. For example, the processing circuitry 114 may include a differential amplifier 520, a differential analog-to-digital converter (ADC) 522, a communications interface 524, a processor 526, and/or other circuitry. The differential amplifier 520 may be connected to the first and second conductors 516-1, 516-2 of the electrical interconnect 108. For example, the first and second conductors 516-1, 516-2 may be electrically connected to input nodes or terminals of the differential amplifier 520. The differential amplifier 520 may provide amplified differential output 528 (e.g., an amplification of the pair of signals obtained from the piezoelectric material 502). The differential output may include biological vibrations sensed by the piezoelectric material 502. As discussed with reference to FIGS. 1 and 3, the differential output may have a frequency bandwidth that includes (e.g., intersects or crosses) an AC line frequency.

In some embodiments, the differential amplifier 520 may be a differential charge amplifier. In other embodiments, the differential amplifier 520 may be a transimpedance amplifier (TIA). When using a TIA, the piezoelectric material 502 may be considered a current source instead of a charge source. A TIA may provide a flatter response over a greater range of frequencies than a differential charge amplifier (i.e., a TIA may provide satisfactory amplification over a greater frequency bandwidth).

In general, the more symmetry that can be maintained in the physical layout of the sensor system 500, from the first and second electrodes 506-1, 506-2 through the output of the differential amplifier 520, the better fidelity of the amplified output.

The differential ADC 522 may be configured to digitize the differential output of the differential amplifier 520. The differential ADC 522 may combine (subtract) the differential signals or differential output of the differential amplifier 520. The digitized differential output may be stored in an optional memory on-board the processing module 106 and/or transmitted (e.g., streamed) to another device via the communications interface 524. In some cases, the communications interface 524 may include a Wi-Fi and/or Bluetooth interface. An optional processor 526 or other circuitry may control operation of the differential amplifier 520, differential ADC 522, communications interface 524, memory, and/or other components of the processing module 106.

In some embodiments, the processor 526 of the processing circuitry 114, a processor of the device 112 (see, FIG. 1), or a processor of yet another device may identify at least a first vibration included in the digitized differential output of the differential ADC 522. The same or a different processor may then pattern match the first vibration to any of a number of known biological vibrations, including, for example, any of the biological vibrations described with reference to FIGS. 3 and 4.

FIG. 6 illustrates how measured vibrations, including biological vibrations, may be amplified by the processing circuitry described with reference to FIGS. 1 and 5, while an AC line frequency or other background noise may be canceled by the processing circuitry. In particular, a first graph 600 shows how AC line noise may be sensed by a differential piezoelectric sensor, such as one of the vibration sensors described with reference to FIG. 1, 2, or 5. As shown, first and second electrodes of the vibration sensor may sense the AC line noise in-phase, such that a subtraction of one signal from the other results in no signal or a direct current (DC) signal being output from a differential ADC, as shown in a second graph 610.

A third graph 620 shows how a vibration (e.g., a biological vibration) may be measured or sensed by the same differential piezoelectric sensor. As shown, the first and second electrodes may sense the vibration out-of-phase, such that a subtraction of one electrode's signal from the other results in an amplified signal being output from the differential ADC, as shown in a third graph 630.

FIG. 7A shows, in exploded form, an example more detailed cross-section of the sensor stack described with reference to FIG. 5. Like components are therefore referred to by like reference numerals in FIGS. 5 and 7A. FIG. 7B shows the cross-section of FIG. 7A in assembled form.

Similar to the sensor stack described with reference to FIG. 5, the sensor stack 700 includes a piezoelectric material 502; first and second electrodes 506-1, 506-2 connected to opposite sides 504-1, 504-2 of the piezoelectric material 502; first and second electromagnetic noise shields 510-1, 510-2; and first, second, third, and fourth thermoplastic polymer resins 512-1, 512-2, 514-1, 514-2. The sensor stack 700 also includes various PSAs.

A first PSA 702-1 may be disposed on the first electrode 506-1, or between the first electrode 506-1 and the first thermoplastic polymer resin 512-1. The first thermoplastic polymer resin 512-1 may be disposed on the first PSA 702-1, and may be coupled to the first electrode 506-1 (and in some areas, to the piezoelectric material 502) by the first PSA 702-1. A second PSA 702-2 may be disposed on the second electrode 506-2, or between the second electrode 506-2 and the second thermoplastic polymer resin 512-2. The second thermoplastic polymer resin 512-2 may be disposed on the second PSA 702-2, and may be coupled to the second electrode 506-2 (and in some areas, to the piezoelectric material 502) by the second PSA 702-2.

A third PSA 702-3 may be disposed on the first electromagnetic noise shield 510-1, or between the first electromagnetic noise shield 510-1 and the third thermoplastic polymer resin 514-1. The third thermoplastic polymer resin 514-1 may be disposed on the third PSA 702-3, and may be coupled to the first electromagnetic noise shield 510-1 (and in some areas, to the first thermoplastic polymer resin 512-1) by the third PSA 702-3. A fourth PSA 702-4 may be disposed on the second electromagnetic noise shield 510-2, or between the second electromagnetic noise shield 510-2 and the fourth thermoplastic polymer resin 514-2. The fourth thermoplastic polymer resin 514-2 may be disposed on the fourth PSA 702-4, and may be coupled to the second electromagnetic noise shield 510-2 (and in some areas, to the second thermoplastic polymer resin 512-2) by the fourth PSA 702-4.

In some alternative embodiments, the third thermoplastic polymer resin 514-1 and third PSA 702-3 may be combined, and/or the fourth thermoplastic polymer resin 514-2 and fourth PSA 702-4 may be combined.

As shown in FIG. 7A, the various conductive elements of the sensor stack 700 may have different widths. They may also have different lengths. In some cases, the electrodes 506-1, 506-2 may have widths and/or lengths that are narrower than those of the electromagnetic noise shields 510-1, 510-2, so that the electrodes 506-1, 506-2 are better shielded by the electromagnetic noise shields 510-1, 510-2. In other cases, the electromagnetic noise shields 510-1, 510-2 may have widths and/or lengths that are the same as those of the electrodes 506-1, 506-2.

FIG. 7C shows an example of the sensor interface described with reference to FIG. 5, in the context of the sensor stack described with reference to FIGS. 7A-7B. Although the electrodes 506-1, 506-2 and first electromagnetic noise shield 510-1 are shown adjacent to one another in the plan view 710, the electrodes 506-1, 506-2 and electromagnetic noise shields 510-1, 510-2 may be stacked as shown in FIG. 7A and the plan view 712. In the plan view 712, the second electromagnetic noise shield 510-2 is not illustrated because it is stacked directly under the first electromagnetic noise shield 510-1.

In the sensor interface 714, each of the first and second electrodes 506-1, 506-2 are re-routed (to the left or to the right), so that the signals they carry are also routed to the left and right, and so that the conductors of an electrical interconnect may be soldered or otherwise connected to the first and second electrodes 506-1, 506-2. The electromagnetic noise shields 510-1, 510-2 may extend between the re-routed electrodes 506-1, 506-2, and may widen to extend over portions of the re-routed electrodes 506-1, 506-2. The symmetry of the sensor interface 714 (at least from a plan perspective) can help maintain the differential integrity of the signals carried on the first and second electrodes 506-1, 506-2. In some cases, the end portions of the electrodes 506-1, 506-2 and/or electromagnetic noise shields 510-1, 510-2 may be raised or lowered to a common plane, using vias or other conductive transitions. The common plane may be variously defined by the first or second thermoplastic polymer resin 512-1, 512-2, a flex circuit, a printed circuit board (PCB), or other non-conductive element.

FIG. 8A shows, in exploded form, an example more detailed cross-section of the sensor stack described with reference to FIG. 7A. Like components are therefore referred to by like reference numerals in FIGS. 7A and 8A.

Similar to the sensor stack described with reference to FIG. 7A, the sensor stack 800 includes all of the elements described with reference to FIG. 7A. However, the sensor stack 800 also includes a capacitive touch sensor electrode 802. The capacitive touch sensor electrode 802 may be disposed in a same layer of the sensor stack 800 as the first electromagnetic noise shield 510-1, but may be electrically insulated from the first electromagnetic noise shield 510-1.

The sensor stack 800 also includes a third electromagnetic noise shield 804, which may be positioned between the piezoelectric material 502 and capacitive touch sensor electrode 802 (or more specifically, between the piezoelectric material 502 and the first PSA 702-1). The third electromagnetic noise shield 804 may be electrically insulated from the piezoelectric material 502 and the capacitive touch sensor electrode 802. The first and third electromagnetic noise shields 510-1, 804 provide at least some noise mitigation between the piezoelectric material 502 and the capacitive touch sensor electrode 802, and at least some noise mitigation between the electrode 506-1 and the capacitive touch sensor electrode 802.

In some embodiments, a self-capacitance of the electrode 802 may be sensed to determine whether a user's finger, torso, or other body part is proximate to the exterior surface of the third thermoplastic polymer resin 514-1. In some embodiments, a determination that a user is proximate to the capacitive touch sensor electrode 802 can be used to enable the differential amplifier 520 and downstream circuitry described with reference to FIG. 5.

FIGS. 8B-8D show various examples of the sensor interface described with reference to FIG. 5, in the context of the sensor stack described with reference to FIG. 8A. In contrast to the sensor interface described with reference to FIG. 7C, the sensor interfaces described with reference to FIGS. 8B-8D passively output a touch indication obtained from the capacitive touch sensor electrode 802, in addition to a pair of signals obtained from the piezoelectric material by the first and second electrodes 506-1, 506-2.

FIG. 8B shows a non-stacked, plan view 810 of the electrodes 506-1, 506-2 and first electromagnetic noise shield 510-1. Although the electrodes 506-1, 506-2 and first electromagnetic noise shield 510-1 are shown adjacent to one another in the plan view 810, the electrodes 506-1, 506-2 and electromagnetic noise shields 510-1, 510-2 may be stacked as shown in FIG. 8A and the plan view 812. In the plan view 812, the second electromagnetic noise shield 510-2 is not illustrated because it is stacked directly under the first electromagnetic noise shield 510-1.

In the sensor interface 814, each of the first and second electrodes 506-1, 506-2 are re-routed (to the left or to the right), so that the signals they carry are also routed to the left and right, and so that the conductors of an electrical interconnect may be soldered or otherwise connected to the first and second electrodes 506-1, 506-2. The electromagnetic noise shields 510-1, 510-2 may extend between the re-routed electrodes 506-1, 506-2.

The capacitive touch sensor electrode 802 and its electromagnetic noise shield 804 may also extend into the sensor interface 814, with the electromagnetic noise shield 804 positioned between the second electrode 506-2 and the capacitive touch sensor electrode 802 (at least in the plan view 812). In this manner, each of the electrodes 506-1, 506-2, 802 is separated from adjacent electrodes by an electromagnetic noise shield 510-1, 510-2, or 804.

In some embodiments, the stacked portions of the first and second electrodes 506-1, 506-2 and first and second electromagnetic noise shields 510-1, 510-2 may be shifted off-center from the end portions of these elements, so that the majority of the first and second electrodes 506-1, 506-2 and first and second electromagnetic noise shields 510-1, 510-2 are farther away from the capacitive touch sensor electrode 802 and its electromagnetic noise shield 804. This can reduce interference between the sound (vibratory and audio) and touch sensors included in the sensor stack 800.

In some cases, the end portions of the electrodes 506-1, 506-2, 802 and/or electromagnetic noise shields 510-1, 510-2, 804 may be raised or lowered to a common plane, using vias or other conductive transitions. The common plane may be variously defined by the first or second thermoplastic polymer resin 512-1, 512-2, a flex circuit, a PCB, or other non-conductive element.

FIG. 8C shows a non-stacked, plan view 820 of the electrodes 506-1, 506-2 and first electromagnetic noise shield 510-1. Although the electrodes 506-1, 506-2 and first electromagnetic noise shield 510-1 are shown adjacent to one another in the plan view 820, the electrodes 506-1, 506-2 and electromagnetic noise shields 510-1, 510-2 may be stacked as shown in FIG. 8A and the plan view 822. In the plan view 822, the second electromagnetic noise shield 510-2 is not illustrated because it is stacked directly under the first electromagnetic noise shield 510-1.

In the sensor interface 824, each of the first and second electrodes 506-1, 506-2 are re-routed to one side of the electromagnetic noise shields 510-1, 510-2, so that the signals they carry are also routed to one side of the electromagnetic noise shields 510-1, 510-2, and so that the conductors of an electrical interconnect may be soldered or otherwise connected to the first and second electrodes 506-1, 506-2. The electromagnetic noise shields 510-1, 510-2 may extend adjacent the re-routed electrodes 506-1, 506-2.

The capacitive touch sensor electrode 802 and its electromagnetic noise shield 804 may also extend into the sensor interface 824, and may be routed as described with reference to FIG. 8B. In this manner, the electrodes 506-1 and 506-2 may be bordered by electromagnetic noise shields 510-1, 510-2, and 804, and the capacitive touch sensor electrode 802 may be separated from the other electrodes by the electromagnetic noise shield 804.

In some cases, the end portions of the electrodes 506-1, 506-2, 802 and/or electromagnetic noise shields 510-1, 510-2, 804 may be raised or lowered to a common plane, using vias or other conductive transitions. The common plane may be variously defined by the first or second thermoplastic polymer resin 512-1, 512-2, a flex circuit, a PCB, or other non-conductive element.

FIG. 8D shows a non-stacked, plan view 830 of the electrodes 506-1, 506-2 and first electromagnetic noise shield 510-1. Although the electrodes 506-1, 506-2 and first electromagnetic noise shield 510-1 are shown adjacent to one another in the plan view 830, the electrodes 506-1, 506-2 and electromagnetic noise shields 510-1, 510-2 may be stacked as shown in FIG. 8A and the plan view 832. In the plan view 832, the second electromagnetic noise shield 510-2 is not illustrated because it is stacked directly under the first electromagnetic noise shield 510-1.

In the sensor interface 834, the second electrode 506-2 is re-routed to one side of the first electrode 506-1, and each of the first and second electromagnetic noise shields 510-1, 510-2 is re-routed to extend adjacent and between end portions of the first electrode 506-1 and the re-routed second electrode 506-2. The electromagnetic noise shields 510-1, 510-2 may also be routed to extend over the transverse portion of the second electrode 506-2.

The capacitive touch sensor electrode 802 and its electromagnetic noise shield 804 may also extend into the sensor interface 834, and may be routed as described with reference to FIG. 8B. In this manner, each of the electrodes 506-1, 506-2, 802 is separated from adjacent electrodes by an electromagnetic noise shield 510-1, 510-2, or 804.

In some cases, the end portions of the electrodes 506-1, 506-2, 802 and/or electromagnetic noise shields 510-1, 510-2, 804 may be raised or lowered to a common plane, using vias or other conductive transitions. The common plane may be variously defined by the first or second thermoplastic polymer resin 512-1, 512-2, a flex circuit, a PCB, or other non-conductive element.

In the various embodiments described herein, it was indicated that the various thermoplastic polymer resins could be formed as a layer of PET or BoPET. Alternatively, the thermoplastic polymer resins may take other forms, or the thermoplastic polymer resins may be replaced by other materials. Some suitable materials include polyurethane (PU) or thermoplastic polyurethane (TPU) substrates. The PU or TPU substrates may be selected to have relatively less hysteresis and relatively elastic strain when undergoing deformation or strain cycling. In some cases, the substrates may be or include shape memory polymer (SMP) substrates (i.e., PU substrates having properties such as good shape recovery, shape retention, and shock absorption over a wide temperature range of interest). One useful SMP is poly(urethane-oxazolidone) (PUO, also known as oxazolidone-modified PU), which has a relatively linear E_(g)/E_(r) ratio over a wide temperature range, where E_(g) is a glassy state modulus of the PUO, and E_(r) is a rubber modulus of the PUO. The E_(g)/E_(r) ratio and shape recovery of a PUO substrate are generally proportional to the PUO's oxazolidone content.

The various electrodes described herein may include silver (Ag), and in some cases may be or include silver/silver sulfate or silver/silver chloride electrodes. The electrodes may also or alternatively include copper (copper/copper sulfate, copper nickel), mercury (calomel), aluminum, gold (AgNW), or other materials. The electromagnetic noise shields described herein may be formed using the same materials used to form the electrodes, or different materials. In some examples, an electromagnetic noise shield may include silver (Ag) printed on a thermoplastic polymer resin, PU, TPU, SMP, and/or PUO substrate. In some examples, an electromagnetic noise shield may include aluminum (Al) and/or copper (Cu), and/or another metal, sputtered on a thermoplastic polymer resin, PU, TPU, SMP, and/or PUO substrate. An electromagnetic noise shield may also be provided by a conductive fabric.

In some embodiments, all of the thermoplastic polymer resins, electrodes, and electromagnetic noise shields may be selected to have characteristics such as great flexibility, and resilience to fatigue, during repeated use of a device.

FIG. 9 illustrates a method 900 of monitoring biological vibrations of a user. The method 900 may be performed using a vibration sensor, vibration sensor module, or sensor stack described with reference to FIG. 1, 2, 5, 7A, or 8A, and the processing module or other device described with reference to FIG. 1 or 5.

At block 902, the method 900 may include receiving a pair of signals from a pair of electrodes connected to opposite sides of a piezoelectric element, as further described herein.

At block 904, the method 900 may include differentially amplifying the pair of signals to generate a differential output, as further described herein. In some cases, the differential amplification may be performed using a differential charge amplifier or a TIA.

At block 906, the method 900 may include identifying a type of biological vibration included in the differential output, as further described herein. The biological vibration may be any of the biological vibrations described with reference to FIGS. 3 and 4, or some other biological vibration.

At block 908, the method 900 may include outputting an indicator of the type of biological vibration. In some cases, the indicator may be a text alert presented on a display screen, or a haptic or audible notification that a user needs to review further details of the biological vibration or discuss the biological vibration with their doctor.

In some cases, the vibration sensors described herein may be used to opportunistically monitor a user's heart rhythm, by sensing basic heart vibrations (S1 and S2 heart sounds) and/or BCG/SCG vibrations. An irregular rhythm may be detected by pattern matching S1/S2 and/or BCG/SCG heart vibrations to known (possibly learned) arrhythmia vibration patterns.

In some cases, the vibration sensors described herein may be used to classify a user's heart rhythm (e.g., as regular (a sinus rhythm (SR)), irregular (e.g., atrial fibrillation detected, etc.), or inconclusive).

In some cases, the vibration sensors described herein may be used to generate a report of a user's heart rate variability (HRV).

In some cases, the vibration sensors described herein may be used to monitor symptoms associated with asthma (e.g., coughs, wheezes, or nighttime awakenings) and generate, for example, a nightly index, trends by week, month, or other time period, and so on. In some cases, incidences of a particular biological vibration or event may be counted. For example, a number of cough sounds, wheeze sounds, or snoring episodes may be counted by a processor or other circuit as a user sleeps.

The foregoing description, for purposes of explanation, uses specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art, after reading this description, that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of the specific embodiments described herein are presented for purposes of illustration and description. They are not targeted to be exhaustive or to limit the embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art, after reading this description, that many modifications and variations are possible in view of the above teachings.

As described above, one aspect of the present technology is the gathering and use of data available from various sources, including data that may be indicative of a user's biological vibrations or sounds, and/or data that may identify the person from which such biological vibrations or sounds were obtained. The present disclosure contemplates that, in some instances, this gathered data may include personal information data that uniquely identifies a user or can be used to identify, diagnose, classify, locate, or contact a specific person. Such personal information data can include demographic data, location-based data, telephone numbers, email addresses, home addresses, data or records relating to a user's health or level of fitness (e.g., vital sign measurements, medication information, exercise information), date of birth, or any other identifying or personal information.

The present disclosure recognizes that the use of such personal information data, in the present technology, can be used to the benefit of users. For example, the personal information data can be used to activate or deactivate various functions of a user's device, or gather health, medical, or fitness information that may be used to diagnose or assist the user. Further, other uses for personal information data that benefit the user are contemplated by the present disclosure. For instance, health, medical, and fitness data may be used to provide insights into a user's general wellness, or may be used as positive feedback to individuals using technology to pursue wellness goals.

The present disclosure contemplates that the entities responsible for the collection, analysis, disclosure, transfer, storage, or other use of such personal information data will comply with well-established privacy policies and/or privacy practices. In particular, such entities should implement and consistently use privacy policies and practices that are generally recognized as meeting or exceeding industry or governmental requirements for maintaining personal information data private and secure. Such policies should be easily accessible by users, and should be updated as the collection and/or use of data changes. Personal information from users should be collected for legitimate and reasonable uses of the entity and not shared or sold outside of those legitimate uses. Further, such collection/sharing should occur after receiving the informed consent of the users. Additionally, such entities should consider taking any needed steps for safeguarding and securing access to such personal information data and ensuring that others with access to the personal information data adhere to their privacy policies and procedures. Further, such entities can subject themselves to evaluation by third parties to certify their adherence to widely accepted privacy policies and practices. In addition, policies and practices should be adapted for the particular types of personal information data being collected and/or accessed and adapted to applicable laws and standards, including jurisdiction-specific considerations. For instance, in the US, collection of or access to certain health data may be governed by federal and/or state laws, such as the Health Insurance Portability and Accountability Act (HIPAA); whereas health data in other countries may be subject to other regulations and policies and should be handled accordingly. Hence different privacy practices should be maintained for different personal data types in each country.

Despite the foregoing, the present disclosure also contemplates embodiments in which users selectively block the use of, or access to, personal information data. That is, the present disclosure contemplates that hardware and/or software elements can be provided to prevent or block access to such personal information data. For example, in the case of advertisement delivery services, the present technology can be configured to allow users to select to “opt in” or “opt out” of participation in the collection of personal information data during registration for services or anytime thereafter. In another example, users can select not to provide health, medical, or fitness data to targeted content delivery services. In yet another example, users can select to limit the length of time personal information data is maintained or entirely prohibit the development of a diagnosis based on such personal information data. In addition to providing “opt in” and “opt out” options, the present disclosure contemplates providing notifications relating to the access or use of personal information. For instance, a user may be notified upon downloading an app that their personal information data will be accessed and then reminded again just before personal information data is accessed by the app.

Moreover, it is the intent of the present disclosure that personal information data should be managed and handled in a way to minimize risks of unintentional or unauthorized access or use. Risk can be minimized by limiting the collection of data and deleting data once it is no longer needed. In addition, and when applicable, including in certain health related applications, data de-identification can be used to protect a user's privacy. De-identification may be facilitated, when appropriate, by removing specific identifiers (e.g., date of birth, etc.), controlling the amount or specificity of data stored (e.g., collecting location data at a city level rather than at an address level), controlling how data is stored (e.g., aggregating data across users), and/or other methods.

Therefore, although the present disclosure broadly covers use of personal information data to implement one or more various disclosed embodiments, the present disclosure also contemplates that the various embodiments can also be implemented without the need for accessing such personal information data. That is, the various embodiments of the present technology are not rendered inoperable due to the lack of all or a portion of such personal information data. For example, content can be selected and delivered to users by inferring preferences based on non-personal information data or a bare minimum amount of personal information, such as the content being requested by the device associated with a user, other non-personal information available to the content delivery services, or publicly available information. 

What is claimed is:
 1. A sensor system, comprising: a sensor stack, including, a piezoelectric material having a first side opposing a second side; a first electrode connected to the first side; and a second electrode connected to the second side; a differential amplifier coupled to the first and second electrodes and configured to generate a differential output indicative of vibrations sensed by the piezoelectric material; an analog-to-digital converter configured to digitize the differential output; and a processor configured to identify a type of biological vibration included in the digitized differential output.
 2. The sensor system of claim 1, wherein: the sensor stack further includes, a first electromagnetic noise shield disposed on the first side of the piezoelectric material and electrically insulated from the piezoelectric material and the first electrode, with the first electrode disposed between the piezoelectric material and the first electromagnetic noise shield; and a second electromagnetic noise shield disposed on the second side of the piezoelectric material and electrically insulated from the piezoelectric material and the second electrode, with the second electrode disposed between the piezoelectric material and the second electromagnetic noise shield.
 3. The sensor system of claim 2, wherein: the sensor stack further includes, a capacitive touch sensor electrode, disposed in a same layer of the sensor stack as the first electromagnetic noise shield, and electrically insulated from the first electromagnetic noise shield; and a third electromagnetic noise shield positioned between the piezoelectric material and the capacitive touch sensor electrode, and electrically insulated from the piezoelectric material and the capacitive touch sensor electrode.
 4. The sensor system of claim 3, further comprising: a sensor interface disposed between the sensor stack and the differential amplifier and configured to passively output a pair of signals obtained from the piezoelectric material by the first and second electrodes, and a touch indication obtained from the capacitive touch sensor electrode.
 5. The sensor system of claim 2, wherein: the sensor stack further includes, a first pressure-sensitive adhesive (PSA) disposed on the first electrode; a first thermoplastic polymer resin disposed on the first PSA; a second PSA disposed on the second electrode; and a second thermoplastic polymer resin disposed on the second PSA; the first electromagnetic noise shield is disposed on the first thermoplastic polymer resin; and the second electromagnetic noise shield is disposed on the second thermoplastic polymer resin.
 6. The sensor system of claim 5, wherein: the sensor stack further includes, a first non-conductive sensor stack cover disposed on the first electromagnetic noise shield; and a second non-conductive sensor stack cover disposed on the second electromagnetic noise shield.
 7. The sensor system of claim 1, further comprising a sensor interface, disposed between the sensor stack and the differential amplifier, that re-routes at least one of: the first electrode or the second electrode.
 8. The sensor system of claim 1, further comprising a sensor interface, disposed between the sensor stack and the differential amplifier, that re-routes at least one signal received from at least one of the first electrode or the second electrode.
 9. The sensor system of claim 1, wherein the piezoelectric material comprises a polyvinylidene difluoride (PVDF) material.
 10. The sensor system of claim 1, wherein the first and second electrodes are configured to generate a pair of signals having a frequency bandwidth including an alternating current (AC) line frequency.
 11. A sensor system, comprising: a sensor, including: a piezoelectric element; and first and second electrodes, respectively connected to first and second opposing surfaces of the piezoelectric element; an electrical interconnect, including: first and second conductors, respectively connected to the first and second electrodes; and a differential amplifier connected to the first and second conductors and providing a differential output indicative of vibrations sensed by the piezoelectric element.
 12. The sensor system of claim 11, wherein the differential amplifier is a differential charge amplifier.
 13. The sensor system of claim 11, wherein the differential amplifier is a transimpedance amplifier.
 14. The sensor system of claim 11, wherein the differential output has a frequency bandwidth including an alternating current (AC) line frequency.
 15. The sensor system of claim 11, further comprising: an analog-to-digital converter configured to digitize the differential output; and a communications interface configured to transmit the digitized differential output to a remote device.
 16. The sensor system of claim 11, further comprising: an analog-to-digital converter configured to digitize the differential output; and a processor configured to: pattern match a vibration pattern in the digitized differential output to one of: a crackle sound, or a wheeze sound, or a cough sound, or a snore sound, or a respiration sound.
 17. The sensor system of claim 11, further comprising: an analog-to-digital converter configured to digitize the differential output; and a processor configured to: pattern match a vibration pattern in the digitized differential output to one of: a type of heart murmur, or a S1, S2, S3, or S4 heart sound.
 18. A method of monitoring biological vibrations of a user, comprising: receiving a pair of signals from a pair of electrodes connected to opposite sides of a piezoelectric element; differentially amplifying the pair of signals to generate a differential output; identifying a type of biological vibration included in the differential output; and outputting an indicator of the type of biological vibration.
 19. The method of claim 18, wherein the type of biological vibration is a crackle sound or a wheeze sound.
 20. The method of claim 18, wherein the differential amplification is performed using a transimpedance amplifier. 